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British actress Sienna Miller was left shaking and sobbing after filming multiple sex scenes with heartthrob Ben Affleck in a nine-hour marathon.

Miller -- who co-stars in the actor’s latest project, Live By Night -- told E! The duo get along like brother and sister but the marathon was too much.

"Ben and I are like brother and sister, thank God, so there was no awkwardness. There was just a lot of stupid giggling. He's very professional—I am not, but he is," Miller said.

She added: "There was a montage in the script saying we did it everywhere: in the car, in the bar...I was like, 'That's an entire day of just love scenes! OK. How do we do this?'

"Obviously, by the time nine hours of it has gone past, I was shaking with tears running down my face. I mean, I can't tell you – but you have to laugh. Ben is just professional. It is what it is."

In the new movie, set in the 1920s, she plays an Irish vixen named Emma Gould.

Affleck also directs and instructed the crew to keep the camera rolling. But after hours of faux sex, Miller had enough.

"This happened three times, and by the third I [finally said], 'Are you joking?'" Miller said. "And then I was like, 'I don't know what you're trying to tell people, Ben, about your sexual prowess – your abilities.'"

Despite the agony of it all, Miller adds that there were a lot of laughs.

"There will be some outtakes from that where I have to walk out of the room because I just have tears running down my face," she said.